Propylene is an important basic raw material for synthetic resins such as polypropylene and for petrochemical products, and is used widely such as for automobile bumpers, food containers, films, and medical instruments.
Isopropyl alcohol produced from plant-derived raw materials can be converted to propylene through a dehydration process. Therefore, isopropyl alcohol is a promising carbon-neutral raw material for propylene. Acetone is also widely used as solvents and raw materials for plastics. Kyoto Protocol called for industrialized nations to reduce their total carbon dioxide emissions from 1990 levels by 5 percent by 2008-2012. Therefore, carbon-neutral propylene is currently extremely important due to its versatility, in view of the global environment.
Bacteria that assimilate plant-derived raw materials and produce isopropyl alcohol are already known. For example, WO 2009/008377 discloses a bacterium that is modified to produce isopropyl alcohol using glucose as a raw material, and describes that the bacterium has excellent properties as a biocatalyst for industrial production due to its high selectivity for isopropyl alcohol.
In isopropyl alcohol-producing Escherichia coli, because the raw material for isopropyl alcohol is glucose, a great number of compounds formed by glycolysis and catabolism can all be by-products. However, these compounds are essential substances for the growth of Escherichia coli in some cases, and, therefore, the amount of glucose consumed by these side reactions cannot be completely eliminated. Accordingly, various studies have been carried out with a view to minimizing the by-products and increasing the amount of isopropyl alcohol produced.
For example, WO 2009/008377 pamphlet discloses an isopropyl alcohol-producing bacterium to which acetoacetate decarboxylase, isopropyl alcohol dehydrogenase, CoA transferase and thiolase genes have been introduced, and which is capable of producing isopropyl alcohol form a plant-derived raw material. It is described that the capacity of the isopropyl alcohol-producing bacterium provides a production rate of 0.6 g/L/hr and an accumulation amount of 28.4 g/L.
WO 2009/049274 and Appl. Environ. Biotechnol., 73(24), pp. 7814-7818, (2007) disclose an Escherichia coli variant to which acetyl-CoA acetyltransferase, acetoacetyl-CoA transferase, acetoacetate decarboxylase and secondary alcohol dehydrogenase genes have been introduced, and which produces isopropyl alcohol. It is described that the capacity of the bacteria provides a production rate of 0.4 g/L/hr, a yield of 43.5%, and an accumulation amount of 4.9 g/L.
WO 2009/028582 discloses an Escherichia coli variant to which acetoacetate decarboxylase, isopropyl alcohol dehydrogenase, acetyl CoA:acetate CoA-transferase and acetyl-CoA acetyltransferase genes have been introduced, and which produces isopropyl alcohol. It is described that the capacity of the bacterium provides an accumulation amount of 9.7 g/L.
Appl. Microbiol. Biotechnol., 77(6), pp. 1219-1224, (2008) discloses an Escherichia coli variant to which thiolase, CoA-transferase, acetoacetate decarboxylase and primary-secondary alcohol dehydrogenase genes have been introduced, and which produces isopropyl alcohol. It is described that the capacity of the bacterium provides a production rate of 0.6 g/L/hr, a yield of 51% and an accumulation amount of 13.6 g/L.
WO 2009/103026 discloses an Escherichia coli variant to which acetoacetate decarboxylase, acetyl CoA:acetate CoA-transferase, acetyl-CoA acetyltransferase and isopropyl alcohol dehydrogenase genes have been introduced, and which is capable of producing isopropyl alcohol. It is described that the bacterium is expected to have a capacity that provides a yield of 50%, a production rate of 0.4 g/L/hr and a final production amount of 14 g/L.
WO 2009/247217 discloses an Escherichia coli variant to which acetoacetate decarboxylase, CoA transferase, thiolase and 2-propyl alcohol dehydrogenase genes have been introduced, and which is capable of producing isopropyl alcohol. It is described that the capacity of the bacterium provides a final production amount of 2 g/L.
Here, isopropyl alcohol dehydrogenase, secondary alcohol dehydrogenase, primary-secondary alcohol dehydrogenase and 2-propyl alcohol dehydrogenase are enzymes that have different names but catalyze the same reaction. CoA transferase, acetoacetyl-CoA transferase, acetyl CoA:acetate CoA-transferase and CoA transferase are enzymes that have different names but catalyze the same reaction. Acetoacetic acid decarboxylase and acetoacetate decarboxylase are enzymes that have different names but catalyze the same reaction. Thiolase and acetyl-CoA acetyltransferase are enzymes that have different names but catalyze the same reaction. Accordingly, although the productivity of the isopropyl alcohol-producing Escherichia coli variants disclosed in these documents varies, the enzymes utilized for producing isopropyl alcohol are equivalent to the four types of enzymes of acetoacetate decarboxylase, isopropyl alcohol dehydrogenase, CoA transferase and thiolase, which are described in WO 2009/008377. In a case in which it is desired to improve the productivity or yield, these four types of enzymes have been examined thus far.
Japanese Patent Application Laid-Open (JP-A) No. 5-260979 describes that, in Bacillus subtillis, disruption of GntR gene possessed by the Escherichia coli improves production of D-ribose.
Further, with regard to a method for converting isopropyl alcohol into acetone, a copper-based catalyst is used as a solid catalyst for production of acetone through dehydrogenation of isopropyl alcohol in JP-A No. 7-53433 and JP-A No. 11-335315. Moreover, a catalyst obtained by physical mixing of zinc oxide fine particles and zirconium oxide fine particles is used in UK Patent No. GB665376. It is known that impurities are generally contained when a substance is produced using a microorganism. In this regard, none of these techniques is a production method using microorganisms, and, therefore, does not describe that impurity-containing isopropanol is used as a raw material
Acetone can easily be converted into isopropanol by hydrogenation. A process has been proposed (see, for example, JP-A No. 2-174737) which includes obtaining propylene from the isopropanol via a dehydration reaction, and thereafter obtaining cumene by allowing the propylene to react with benzene, that is, a process in which acetone is reused as a raw material for the Cumene method by being converted into propylene via two-step reactions.
In the re-usage as described above, there is a need for establishment of an industrial and practical method for producing propylene from acetone with high selectivity. A method is also known (see, for example, East Germany Patent No. DD84378) which includes carrying out a hydrogenation reaction of acetone at 400° C. in the presence of a Cu (25%)-zinc oxide (35%)-aluminum oxide (40%) catalyst to obtain propylene. However, although the reaction temperature in this method is high (400° C.), the conversion rate of acetone is low (89%). In addition, since a side reaction that generates propane via hydrogenation of propylene occurs in the method, the propylene selectivity is also insufficient (89%).